JPH04326033A - Pressure or acceleration sensor - Google Patents

Abstract

PURPOSE: To obtain a sensor for measuring pressure and acceleration. CONSTITUTION: The sensor for measuring pressure or acceleration comprises a structured silicon carrier 10, and a frame 11 having a displaceable membrane 12 formed on the first major surface thereof. The membrane 12 has a reinforcing region and a first part structure is coupled with the membrane 12 in the reinforcing region. At least a part of the membrane 12 extends over the frame 11 and forms the electrode of a capacitor. At least one counter electrode 161, 162 of the capacitor is arranged oppositely to the first part structure in the region of the frame 11.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor for measuring pressure or acceleration having a single-crystal silicon carrier, the silicon carrier having an array of thin films deposited on its first main surface. The thin film layer is configured with a structure having at least one first partial structure, which first partial structure is oriented parallel to the first main surface of the silicon carrier, and which is oriented parallel to the first main surface of the silicon carrier. The present invention relates to a sensor in which a gap exists between a structure and a main surface.

0002

[Prior art] “Fine Grained Poly
silicon and its application
on to Planar PressureTran
sducers”, H. Gruckel et al., Tran
sducer, 1987, pp. 277-282,
A method for manufacturing a pressure sensor with surface microtechnology is described. In this manufacturing method, a three-dimensional sensor structure (for example a diaphragm structure, a tongue structure or a bridge structure) is formed by an array of separated thin films on a single crystal silicon substrate. A displaceable or deformable sensor structure is obtained by first applying a structured silicon oxide layer to a substrate and subsequently separating a polysilicon layer onto this silicon oxide layer. By structuring the polysilicon layer and lateral bottom etching, the structured silicon oxide layer is removed and the sensor structure is exposed in the polysilicon layer. This document also describes the effects of different process parameters of the manufacturing method on the material properties of the sensor structure. The functionality and reliability of this type of sensor depends mostly on the properties of the material, such as the elastic modulus. The displaceable or deformable element of the sensor is manufactured from this material.

Unpublished German patent application P4022495
．． Furthermore, a method for manufacturing a sensor structure of a three-layer silicon wafer is known from No. 3. Here, retaining webs for the vibrating seismic mass are constructed on both external layers of the silicon wafer.

ADVANTAGES OF THE INVENTION The sensor of the invention with the features of claim 1 combines the advantages of sensors manufactured with volumetric microtechnology and the advantages of sensors manufactured with surface microtechnology, and combines the advantages of sensors manufactured with volumetric microtechnology and with the advantages of sensors manufactured with surface microtechnology. It has the advantage of avoiding the disadvantages of The sensor of the invention has a movable diaphragm structured from a monocrystalline silicon carrier, which movable diaphragm is provided with a reinforcement region. This reinforcement region can be produced simply and with good reproducibility by means of volumetric microtechnology. The diaphragm is constructed on a first main surface of the silicon carrier, onto which a thin film array is applied. These thin films constitute a structure having at least one partial structure. This substructure is oriented parallel to the silicon carrier. This is particularly advantageous if realized with surface microtechnology. The first substructure forms the electrode of the capacitor and is connected to the diaphragm in the region of the reinforcement. The first substructure extends at least partially beyond the diaphragm and above the fixed frame of the diaphragm. At least the counter electrode of the capacitor is arranged here. The distance between the electrodes of the capacitor is very small due to the good process characteristics of the surface microtechnology method. This results in a sensor with a small construction volume and a high constant capacity compared to the construction volume. Particularly preferably, the acceleration or pressure applied to the sensor causes a deformation of the monocrystalline diaphragm, but the substructure used as the electrode is not deformed. This substructure is not deformed but displaced;
This is detected capacitively. This is because this substructure is fixed in the region of the reinforcement of the diaphragm to the frame, in particular to the structure attached thereto, for example to the counterelectrode. The structures deposited on the silicon carrier with surface microtechnology are therefore not deformed and are used exclusively for detecting deformations of the single-crystal diaphragm. The stiffness of this diaphragm depends first of all on the very well defined material parameters of single-crystal silicon. Therefore, it is possible to easily manufacture a sensor having a predetermined and reproducible sensitivity. This simple sensor structure is particularly IC compatible.

Advantageous embodiments of the sensor according to claim 1 are possible with the measures set out in the dependent claims. Advantageously, the sensor according to the invention is realized simply by the second substructure as a differential capacitor arrangement with measuring signal amplification, which is sufficient even without an additional bonded wafer. It is also particularly advantageous for the surface structure of the sensor to be structured from a polysilicon layer or a monocrystalline silicon layer. This is because the techniques for this purpose are well known and can be easily operated. Furthermore, it is advantageous to design the diaphragm in such a way that it has an additional mass 13 in the region of the reinforcement. This configuration on the one hand prevents the diaphragm from deforming without bending in the region of the reinforcement, and on the other hand amplifies and linearizes the measuring effect. The use of a silicon carrier is particularly advantageous if the silicon carrier is structured by anisotropic etching. This silicon carrier has several layers between which doping migration occurs. The electrical terminals of the electrodes of the capacitor as well as the first part of the silicon carrier
The counterelectrode arranged on the main surface of the silicon carrier is simply realized by diffusion on the first main surface of the silicon carrier. For the functioning of the sensor according to the invention, it is advantageous if the surface structure of the sensor is hermetically sealed to the first main surface of the silicon carrier. This is preferably achieved by a cover made of polysilicon or monocrystalline silicon. Inside the cover there is a predetermined pressure, preferably a vacuum, which determines the degree of damping of the sensor. The cover also serves as a protection against dirt and damage to the sensor due to external influences. In order to avoid that the electrodes of the capacitor device adhere to each other, for example by adhesion, a low-potential passivation layer is applied over the entire surface structure and on the first main surface of the silicon carrier, at least in the region of this structure. , preferably a nitride layer. It is particularly advantageous to construct the capacitor structure of the sensor exclusively on the silicon carrier surface and the polysilicon layer. In the present invention, this is configured as follows. That is, a part of the central electrode is formed as a surface structure and a part is formed on the first main surface of the silicon carrier, and the first counter electrode is formed as a surface structure on the main surface of the silicon carrier. formed above a portion of the central electrode as a surface structure partially diffused below and fixedly stretched by a second counter electrode;
This central electrode is constructed in such a way that it is diffused into the first main surface of the reinforcement region of the silicon carrier.

When using the sensor according to the invention as an acceleration sensor, it is advantageous to provide a tear in the diaphragm around the additional mass. Thereby, the additional mass is suspended only by the web configured in the diaphragm. In order to reduce the lateral sensitivity of such an acceleration sensor, an additional mass is additionally connected to the frame below the second main surface of the silicon carrier. It is advantageous to constantly perform a functional test of the acceleration sensor. To this end, a lower cover is applied to the underside of the silicon carrier. This lower cover has a cavity in the region of the additional mass. A first excitation electrode is arranged in the area of the additional mass below the sensor. A second excitation electrode is arranged on the bottom of the cavity opposite thereto. Furthermore, means are provided for applying a voltage between the two electrodes. This allows the additional mass to be electrostatically displaced. This displacement, like the acceleration, is detected by structures arranged on the surface of the silicon carrier. This constant functional check is particularly advantageous for acceleration sensors of safety devices.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, a single crystal silicon carrier is designated by 10. The silicon carrier is 1 as in this example.
It can consist of one layer, but it can also consist of several layers, with doping migration occurring between the layers. The silicon carrier 10 is structured. The silicon carrier therefore has a frame 11 and a diaphragm 12. The diaphragm 12 is constructed on the first main surface of the silicon carrier 10 and has a reinforcement in its central region. An additional mass body 13 is constructed within the reinforcement section. When acceleration or pressure acts perpendicularly to the carrier plane, the diaphragm is displaced with deformation in its edge region. A structure 50 is applied to the first main surface of the silicon carrier 10 . This structure has a plurality of partial structures. Structure 50
is advantageously manufactured from a polysilicon layer or a monocrystalline silicon layer. Methods for manufacturing such structures are sufficiently known from the prior art and therefore will not be described in detail here. The first partial structure of the structure 50 is the frame 21
Consisted of. Tongue pieces 221 and 222 protrude from this pedestal. These tongues are oriented parallel to the first major surface of the silicon carrier. The first structure can also be constituted by a pedestal 21 with a cover plate. This cover plate projects beyond the pedestal on its entire surface and has the same function as the tongues 211, 222. The pedestal 21 is arranged in the region of the reinforcement of the diaphragm 12. The tongues 221 and 222 extend above the frame 11 beyond the diaphragm 12. A gap exists between the tongues 221, 222 and the first main surface of the silicon carrier 10. Two further substructures of the structure 50 are formed by frames 311 , 312 arranged in the area of the frame 11 . Tongue pieces 321 and 322 protrude from these frames, respectively. The tongues 321 , 322 are likewise oriented parallel to the first main plane of the silicon carrier, but in the direction of the diaphragm 12 . Due to the height of the pedestals 311 and 312, they are attached to the tongues 221 of the first structure.
, 222. Tongue piece 22 of the first structure
1, 222 and the tongue pieces 321, 322 of the second structure also have gaps. The first structure with tongues 221 and 222 forms the central electrode of the differential capacitor. The central electrodes are connected via a conductor 18 . The conductor lines are configured in the form of a connecting diffusion on the first main surface of the silicon carrier 10 in the area of the pedestal 21 . Tongue pieces 221, 222 of the first structure
Diffused counter electrodes 161 and 162 are arranged on the first main surface of the silicon carrier 10, respectively. However, this counterelectrode can also be realized, for example, in the form of surface metallization. The two further substructures constitute the second opposing electrodes 301, 302 of the differential capacitor. These counter electrodes are likewise connected in contact by conductive wires 171 and 172. These conductors are connected to mounts 311 and 312.
is diffused into the first main surface of the silicon carrier 10 in the region of . A force acting perpendicularly to the carrier plane on the sensor illustrated in FIG. 1 deforms the edge region of the diaphragm 12 and causes a displacement of the diaphragm 12. At that time, the tongue pieces 221 and 222 used as the center electrode and the first counter electrode 1
The distance between the electrodes 61 and 162 and the second opposing electrodes 301 and 302 also changes. This interval change is detected as a capacitance change of the differential capacitor. It is noted that the structure 50, in particular the central electrode and the counter electrode, is not deformed. Only the monocrystalline silicon diaphragm 12 is deformed, the material is fatigue-free and can be produced very easily and reproducibly.

The sensor shown in FIG.
has. This silicon carrier is the same as the silicon carrier 10 of the sensor shown in FIG. The same reference numerals are therefore used below for corresponding structural elements. A structure 50 (preferably made of porosilicon or monocrystalline silicon) is applied to the silicon carrier 10 as well. Structure 50
have two first partial structures consisting of frames 211 and 212, respectively, and tongues 221 and 222 extending therefrom. The two first substructures are each applied at the edge of the reinforcement region of the diaphragm 12 onto a support 211 and 212 on the first main plane of the silicon carrier 10 . The tongues 221 and 222 are oriented parallel to the first main plane of the silicon carrier 10 and extend beyond the diaphragm 12 to the frame 1.
1 protrudes upward. A gap exists between the tongue pieces 221, 222 and the first main plane of the silicon carrier 10. The two first substructures are electrically conductively connected to each other via an electrode 15 diffused into the diaphragm 12 in the reinforcement region. In the area of the frame 11 each tongue 221, 2
Opposite 22 , first counter electrodes 161 and 162 are diffused into the main plane of silicon carrier 10 . Electrode 15,1
61 and 162 can be realized in other ways, for example by separate polysilicon layers. The second counter electrode 25 is formed by another substructure of the structure 50. This counter-electrode 25 is connected in the form of a bridge from one side of the frame 11 to the opposite side of the frame 11 over the reinforcing part of the diaphragm 12 between the frames 221 and 222 of the two first partial structures.
It is stretched between. In the case of this sensor, the tongue piece 221
and 222 and the frame 21
1 and 212 are used as the center electrode of the differential capacitor with electrode 15 diffused into the diaphragm. The first opposing electrodes 161 and 162 of the differential capacitor are connected to the frame 11.
is placed on the surface of The second counter electrode 25 is arranged on top of the electrode 15 diffused into the diaphragm 12 . In the sensor shown in FIG. 1, the displacement of the diaphragm 12 when a force is applied perpendicularly to the carrier surface is determined by the tongues 221 and 222, which are part of the central electrode of the differential capacitor, the first opposing electrode 161, 162. Furthermore, the distance between the diaphragm 12 and the second opposing electrode 25 also changes. In this case, an electrode 15 is located on the surface of the diaphragm 12 as part of the central electrode. The displacement of the diaphragm 12 is therefore again detected capacitively by the differential capacitor arrangement. In contrast to the sensor shown in FIG. 1, the structure 50 of the sensor shown in FIG. With this configuration of structure 50, FIG.
Compared to the configuration of the structure 50 shown in FIG. 1, process steps are saved in the manufacture of the sensor.

FIG. 3 shows a front view of the sensor of FIG. Although the first major surface of the silicon carrier 10 is shown by the structure 50 deposited thereon, the frame 11
, the region of the diaphragm 12 and the reinforcement region 13 with the additional mass 13 are also shown. The tongues 211 and 222 of the first partial structure come out of frames 211 and 222 arranged at the edges of the reinforcing part of the first structure and are configured in the shape of an oar. The tongues 221 , 222 extend beyond the area of the diaphragm 12 and at least partially above the area of the frame 11 . On the frame 11 are tongue pieces 221 and 22.
First opposing electrodes 161 and 162 are arranged opposite to each other. The second partial structure forming the second counterelectrode 25 is stretched over the diaphragm 12 from one side of the frame 11 to the opposite side of the frame 11 in the form of a bridge. The second part structure can be contact-connected, for example by connection diffusion. The second counter electrode 25 is arranged between the frames 211 and 212 of the first partial structure, and above the electrode 15 arranged in the reinforcement region. This electrode 15 makes an electrically conductive connection between the two first substructures. The two first and second substructures are structured from one common layer in this example.

FIG. 4 shows a sensor corresponding to FIGS. 2 and 3, which has a cover 40. In FIG. This cover can be realized, for example, by a polysilicon layer or a monocrystalline silicon layer. This layer protrudes from the entire sensor structure and hermetically seals it off. Therefore, the pressure inside the cover 40 can be adjusted to a predetermined pressure, for example, a vacuum. The pressure determines the damping characteristics of the sensor.

FIG. 5 shows the structure of a sensor according to the invention as an acceleration sensor having a structure 50. In FIG. The structure 50 corresponds to FIGS. 2 and 3. Here, the silicon carrier 10 has an upper layer 8 in which a diaphragm 12 is arranged.
consists of a part of. A lower layer 9 is applied to the underside of the silicon carrier 10 . This lower layer is also preferably a monocrystalline silicon layer. For application of the sensor as an acceleration sensor, the diaphragm 12 is partially etched through. The additional mass 13 is thereby suspended only on the web. Since the additional mass 13 used as a seismic mass has a center of gravity that is not in the plane of the diaphragm 12, the seismic mass 13 is configured in the lower layer 9 and is additionally connected to the frame 11 by a fastening web 14. ing. This measure reduces the sensitivity to lateral accelerations. The realization of this main structure with double-sided pn etch stop limits is already known from the prior art.

FIG. 6 shows an acceleration sensor corresponding to FIG. A lower cover 45 is attached to the lower side of this sensor. The lower cover can be realized, for example, by a silicon wafer or a glass carrier. In the region of the additional mass 13 and the fastening web 14 the lower cover 45 has a cavity 44 . A first excitation electrode 46 is arranged on the lower layer 9 in the region of the additional mass 13 . This excitation electrode can be realized by diffusion or metallization. A second excitation electrode 47 is provided on the bottom surface of the cavity 44 opposite to the first excitation electrode 46.
is covered. This is likewise realized in the form of metallization. By applying a voltage between excitation electrodes 46 and 47, additional mass 13 is electrostatically displaced. This displacement, like the acceleration, can also be detected by the differential capacitor structure on the upper side of the silicon carrier 10. Since the excitation electrodes 46 and 47 are separate from the differential capacitor arrangement, this functional test of the sensor is also possible during operation of the sensor. This is particularly advantageous for acceleration sensors of safety devices.

When realizing the electrodes of the capacitor structure of the sensor according to the invention as illustrated in FIGS. 1 to 6 with surface microtechnology, it is advantageous to use the entire capacitor structure in order to avoid "sticking together". On all sides of the body and to the first main surface of the silicon carrier, a passive layer of low potential, preferably a nitride layer, is separated in the region of the surface structure. This avoids short-circuits of the sensor due to fouling or overloading.

[0015]

According to the present invention, a sensor for measuring pressure and acceleration is obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a sensor of the present invention.

FIG. 2 is a cross-sectional view of another sensor of the invention.

FIG. 3 is a front view of the sensor of FIG. 2;

4 is a sectional view of the covered sensor corresponding to FIGS. 2 and 3; FIG.

FIG. 5 is a cross-sectional view of the acceleration sensor.

6 is a cross-sectional view of the acceleration sensor of FIG. 5 with a functional test function; FIG.

[Explanation of symbols]

10 Single crystal silicon carrier 11 Frame 12 Diaphragm 13 Additional mass body 18 Railway track 21 Mount 50 Structure 161, 162 Counter electrode 221, 222 Tongue piece

Claims (17)

[Claims] 1. A sensor for measuring pressure or acceleration having a monocrystalline silicon carrier, the silicon carrier having an array of thin films deposited on a first major surface, the thin film layer comprising at least one A structure is formed having two first substructures, the first substructures being oriented parallel to the first main surface of the silicon carrier, and the first substructures and the main surface being oriented parallel to each other. In a sensor between which there is an air gap, - the silicon carrier (10) is structured and has a frame (11) with a displaceable diaphragm (12) configured on the first major surface; , - the diaphragm (12) has a reinforcement area, - the first partial structure has a reinforcement area of the diaphragm (12);
2), - the first partial structure extends at least partially above the frame (11) beyond the diaphragm (12); -
the first substructure forms an electrode of a capacitor, - at least one counterelectrode (161, 162) of the capacitor is arranged opposite said first substructure in the region of the frame (11); A pressure or acceleration sensor characterized by: 2. - at least one second substructure is provided, said second substructure comprising a frame (11);
is connected to the silicon carrier (10) in the region of - the at least one second partial structure forms at least one second counterelectrode to the electrode;
The counter electrode includes at least one first counter electrode (161, 1
62) and the electrode as the central electrode form a differential capacitor. 3. Sensor according to claim 1, wherein the structure (50) is structured from a polysilicon layer or a monocrystalline silicon layer. 4. The diaphragm (12) has an additional mass (13) in the region of the reinforcement.
The sensor according to any one of the above. 5. - the silicon carrier (10) comprises an upper layer (8);
5. The sensor according to claim 1, wherein the upper layer comprises a diaphragm (12). 6. - The electrical connections of the electrodes of the capacitor are:
6. The sensor according to claim 1, wherein the sensor is diffused onto the first major surface of the silicon carrier (10). 7. - at least one first of the capacitors;
7. Sensor according to claim 1, wherein the counter electrodes (161, 162) are diffused onto the first main surface of the frame (11). - The structure (50) includes a cover (40)
8. The cover is applied to the first main surface of the silicon carrier (10) and is preferably made of polysilicon or monocrystalline silicon. 1. The sensor according to 1. 9. Sensor according to claim 8, characterized in that there is a predetermined pressure in the cover (40), preferably a vacuum. 10. On all sides of all substructures of the structure 50 and on the first main surface of the silicon carrier (10), at least in the region of the structure 50 there is provided a passive layer with a weak potential, preferably nitride. 10. A sensor according to claim 1, wherein a layer is applied. 11. The at least one second partial structure has at least one pedestal (311, 312) from which at least one second counter electrode (301, 302) configured in the form of a tongue extends. Overhanging, at least 1
The two second partial structures have at least one pedestal (311,
312) to the frame (11);
- at least one second counter-electrode is oriented parallel to the first sub-structure forming the central electrode and extends at least in part above said first sub-structure; 10. The sensor according to any one of items 1 to 10. 12. At least one first partial structure has a cradle (211, 212) from which at least one movable central electrode (221, 212) is configured in the form of a tongue.
222) is overhanging, the at least one first partial structure is connected to the diaphragm (12) via at least one cradle (211, 222), - the at least one cradle (211, 212) is reinforced; at least one movable central electrode (2
21, 222) are oriented parallel to the first main surface of the silicon carrier (10) and project above the frame (11); - in the area of the reinforcement of the diaphragm (12) at least one
two electrodes (15) are arranged, which electrodes are in electrically conductive contact connection with at least one movable central electrode (221, 222), - above the at least one electrode (15) at least one At least one frame (211) of the first partial structure
, 212), a second opposing electrode (25) connected to the frame (11) on both sides and configured in the form of a bridge is arranged as at least one second partial structure. The sensor according to any one of the above. 13. From claim 4, in which the diaphragm (12) is penetrated around the periphery of the additional mass (13), so that the additional mass is suspended only on a web configured in the diaphragm (12). 12. The sensor according to any one of up to 12. 14. - on the second main surface of the silicon carrier ( 10 ) a lower layer ( 9 ), preferably a monocrystalline silicon layer, is applied; - on the lower layer ( 9 ) a fixing web ( 14 ); ) and the fixed web connects the additional mass (13) to the frame (
11) The sensor according to any one of claims 4 to 13, in combination with 11). 15. A lower cover (45) is applied to the lower layer (9), the lower cover having a cavity (44) in the region of the additional mass (13), - the lower layer (9)
in the region of the additional mass (13) at least one first
an excitation electrode (46) is arranged; - opposite the at least one first excitation electrode (46), at least one second excitation electrode (47) is arranged at the bottom of the cavity (44); 15. Sensor according to claim 14, characterized in that means are provided for applying a voltage between the excitation electrodes (46, 47). 16. Sensor according to claim 15, wherein the lower cover (45) is formed from a glass carrier or a silicon carrier. 17. - The pressure supply part is a silicon carrier (10
13. The sensor according to claim 1, wherein the sensor is arranged on the second main surface of the sensor.